This disclosure relates to tower cranes of the type used for vertical lifts in building construction projects and similar applications. The load being lifted must in many instances also be pivoted about the vertical tower axis. In the usual tower crane, pivotal torque is applied to the tower base, and is transmitted upwardly through the tower and horizontally through the boom to the load suspended on a cable. High inertial forces are thereby encountered, which tend to "wind" the tower.
Tower cranes are typically mounted to a relatively short counterweight base, requiring heavy counterweight units to balance the load carried on the boom. To remain erect, the overturning moment exerted by the load must always be less than the counterbalance moment on the tower.
According to the present invention, a rigid interconnection to a remotely spaced counterweight is provided to the vertical tower not only at its lower end, but also at its upper end. Rotational turning forces are applied to both the upper and lower ends of the tower from a self-propelled mobile counterweight unit. The resulting triangular rigid framework connecting the tower and counterweight unit eliminates the torsional twisting forces which would otherwise be applied to the tower by a connection to the counterweight only at its lower end.